One of the major hormones that influences metabolism is insulin, which is synthesized in the beta cells of the islets of Langerhans of the pancreas. Insulin primarily regulates the direction of metabolism, shifting many processes toward the storage of substrates and away from their degradation (for reviews, see e.g. Shepherd, P. R. et al. (1998) Biochem. J. 333: 471-490; Alessi, D. R. & Downes, C. P. (1998) Biochim. Biophys. Acta 1436: 151-164). Insulin is believed to be involved in the transport of glucose and amino acids as well as key minerals such as potassium, magnesium, and phosphate from the blood into cells. Insulin is also believed to regulate a variety of enzymatic reactions within the cells, which involve the synthesis of large molecules from smaller building block units. A deficiency in the action of insulin (diabetes mellitus) can cause severe impairment in (i) the storage of glucose in the form of glycogen and the oxidation of glucose for energy; (ii) the synthesis and storage of fat from fatty acids and their precursors and the completion of fatty-acid oxidation; and (iii) the synthesis of proteins from amino acids.
There are two varieties of diabetes. Type I is insulin-dependent diabetes mellitus (IDDM; formerly referred to as juvenile onset diabetes), for which administration of insulin is required. In this type, insulin is not secreted by the pancreas and hence must be administered. Type II diabetes, i.e. non-insulin-dependent diabetes mellitus (NIDDM), is characterized clinically by hyperglycemia and insulin resistance and is commonly associated with obesity. Type II diabetes is a heterogeneous group of disorders in which hyperglycemia typically results from both an impaired insulin secretory response to glucose and decreased insulin effectiveness in stimulating glucose uptake by skeletal muscle and in restraining hepatic glucose production (insulin resistance). Before diabetes develops, patients generally lose the early insulin secretory response to glucose and may secrete relatively large amounts of proinsulin. In established diabetes, although fasting plasma insulin levels may be normal or even increased in type II diabetes patients, glucose-stimulated insulin secretion is clearly decreased. The decreased insulin levels typically reduce insulin-mediated glucose uptake and fail to restrain hepatic glucose production.
Glucose homeostasis depends upon a balance between glucose production by the liver and glucose utilization by insulin-dependent tissues, such as fat and muscle, and insulin-independent tissues, such as brain and kidney. In type II diabetes, the entry of glucose into fat and muscle is reduced and glucose production in the liver is increased, due to insulin resistance in the tissues.
The receptor tyrosine kinases (RTKs) are a class of cell-surface receptors. The ligands for RTKs include peptide/protein hormones including nerve growth factor (NGF), platelet-derived growth factor (PDGF), epidermal growth factor (EGF), and insulin. Binding of a ligand to an RTK is believed to stimulate the receptor's intrinsic protein-tyrosine kinase activity, which subsequently can stimulate a signal-transduction cascade leading to changes in cellular physiology and patterns of gene expression. RTK signaling pathways have a wide spectrum of functions including regulation of cell proliferation and differentiation, promotion of cell survival, and modulation of cellular metabolism.
The platelet-derived growth factor receptor (PDGFR) and the Fms-like tyrosine kinase 3 (FLT-3) have been implicated in a number of pathologies, especially in various cancers, and are therefore considered as drug targets. Both are members of the class III receptor tyrosine kinase (RTK) family, which also includes the receptors for the stem cell factor (c-KIT), and for the colony stimulating factor 1 (CSF1R). The PDGF receptor is involved in wound healing and regulation of homeostasis of the connective tissue compartment. It is expressed on early stem cells, mast cells, myeloid cells, mesenchymal cells, and smooth muscle cells. Overactivity/-expression of PDGFR has been implicated in malignancies as well as in different diseases involving excessive cell growth such as atherosclerosis and fibrosis. The FLT-3 receptor is crucial for the maintenance, proliferation, and differentiation processes in haematopoiesis. FLT-3 is expressed by normal myeloid and lymphoid early progenitors as well as by leukemic cells. Inhibition of the tyrosine kinase activity of the receptor is a therapeutic concept of current interest in antileukemia drug research. This new approach to the treatment of acute myeloid leukemia (AML) has emerged following evidence that constitutive activation of the FLT-3 receptor plays an important role in the development of this aggressive haematological malignancy for which no effective cure exists at the moment (see e.g. Markovic, A. et al. (2005) Int. J. Biochem Cell Biol. 37(6): 1168-1172).
Ras is a GTP-binding switch protein that acts in a manner similar to a key signaling molecule in pathways triggered by activation of RTKs. In general, Ras-linked RTKs in mammalian cells appear to utilize a highly conserved signal-transduction pathway in which activated Ras induces a kinase cascade that culminates in the activation of MAP kinase (mitogen-activated protein kinase). This serine/threonine kinase, which can translocate into the nucleus, phosphorylates many different proteins including transcription factors that regulate expression of what are considered to be important cell-cycle and differentiation-specific proteins.
The murine MNK1 and MNK2 gene products (“MAP kinase interacting kinase” or “MAP kinase signal-integrating kinase” 1 and 2) are single-domain serine/threonine kinases that share 72% sequence identity (Waskiewicz A. J. et al. (1997) EMBO J. 16: 1909-1920; GenBank Accession Nos. Y11091 and Y11092). Human MNK1 has also been described (Fukunaga, R. et al. (1999) EMBO J. 16: 1921-1933; GenBank Accession No. AB000409). All these three proteins were identified, in part, by their ability to bind tightly to MAP kinases. Both MNK1 and 2 bind the extracellular signal-regulated kinases ERK1 and ERK2, and MNK1 also binds the stress-activated kinase, p38. The eukaryotic initiation factor 4E (eIF4E) has been identified as one of the physiological substrates of MNK1 and MNK2 (Scheper, G. C. et al. (2001) Mol. Cell. Biol. 21: 743-754).
According to the findings of Harris et al. (Blood (2004), vol. 104:5, pp 1314-1323), some eIFs, such as eIF4E, selectively enhance expression of growth-promoting (e.g. cyclin D) and metastasis-related mRNAs (e.g. vascular endothelial growth factor), thus suggesting that translation control through regulation of eiFs may play a role in tumor growth control.
The human mnk2 gene has been identified and characterized through a yeast two-hybrid screen in which the MNK2 protein interacted with the ligand-binding domain of the estrogen receptor (ERβ) (Slentz-Kesler, K. et al. (2000) Genomics 69: 63-71). It was shown that the human mnk2 gene has two C-terminal splice variants, designated mnk2a (GenBank Accession No. AF237775) and mnk2b (GenBank Accession No. AF237776). The two isoforms have been shown to be identical over the first 385 amino acids of the coding sequence and differ only in the final exon, which encodes an additional 80 residues for mnk2a and 29 residues for mnk2b. It was further shown that the MNK2 interaction was selective for estrogen receptor (ER) as opposed to ERI and that the interaction was specific to MNK2b as opposed to MNK2a or MNK1.
WO 02/103361 discloses that MNK2 is involved in the insulin-signaling pathway and features a method for identifying a modulator of glucose uptake. WO 03/037362 suggests that MNK kinases, particularly MNK2 (MNK2a and MNK2b), are involved in the regulation of body-weight and thermogenesis, and thus may be associated with metabolic diseases such as obesity, as well as related disorders such as eating disorder, cachexia, diabetes mellitus, hypertension, coronary heart disease, hypercholesterolemia, dyslipidemia, osteoarthritis, gallstones, and sleep apnea, and disorders related to ROS defense, such as diabetes mellitus, neurodegenerative disorders, and cancer, e.g. cancers of the reproductive organs. According to WO 2005/003785, the MNK kinases are believed to be promising targets for anti-inflammatory therapy.
Obesity is one of the most prevalent bodyweight disorders in the world. Obesity is defined as a body weight more than 20% in excess of the ideal bodyweight. It is associated with an increased risk for cardiovascular disease, hypertension, diabetes, hyperlipidemia and an increased mortality rate. Obesity is considered a condition with potential multiple causes and is characterized by elevated fasting plasma insulin and an exaggerated insulin response to oral glucose intake.
The MNK1 protein has been shown by Worch et al. (Oncogene (2004); 23:9162-9172) to be induced by acute myeloid leukaemia (AML) translocation products, PML-RARα, PLZF-RARα and AML1-ETO, in cell lines, by stabilization of the MNK1 protein. Inhibition of MNK1 enhanced hematopoietic cell differentiation. In AML patients 25 of 99 samples of bone marrow showed MNK1 expression with cytoplasmic localization and in these patients MNK1 expression was associated with the oncogene, c-Myc, protein expression.
Compounds that inhibit Mnk2 are important for the prevention and treatment of diseases and disorders related to bodyweight regulation and thermogenesis. In particular, PCT application WO 03/037362 and references cited therein disclose small molecule inhibitors of Mnk2 such as CGP57380 that are said to be useful for the prevention and treatment of metabolic diseases such as obesity and diabetes.

A clear correlation exists between obesity and type 2 diabetes. Type 2 diabetes, otherwise known as diabetes mellitus, develops most often in obese individuals. It is characterized by hyperglycemia resulting from impaired insulin sensitivity coupled with the body's inability to compensate for increased insulin production, rather than an actual deficiency of insulin secretion as with type 1 diabetes. Type 2 diabetes and obesity are characterized by an overexpression of Mnk2. Therefore inhibition of Mnk2 aids in the treatment and prevention of these two widespread diseases.
Several findings suggest that Mnk2 modulates the RAS/MAP kinase pathway and thereby modulates response to insulin and glucose homeostasis. In mammalian systems, overexpression of Mnk2b results in defects in MAP kinase signaling and glucose uptake (WO 02/103361). Mnk2b overexpression decreases glucose uptake in mouse adipocytes and human neuronal cells in vitro. Glucose uptake in the neuronal cell line can be increased by the knockdown of endogenous Mnk2 using RNAi (RNA interference). As a result of these findings, persons of skill expect that an inhibitor of Mnk2 will be beneficial in limiting blood glucose levels.